Heparin interference in the cerebrospinal fluid protein assay measured with a pyrogallol red-molybdate complex

Increased cerebrospinal fluid (CSF) total protein is a useful indicator of meningeal or central nervous system disease. Occasionally the primary care physicians added heparin to CSF samples to avoid clotting. The aim of this study is to investigate the interference of heparin on CSF total protein measurement.

CSF specimens were collected from 230 in-patients with various diseases and analyzed by the Vitros 950 PROT slide and the Toshiba TBA-120FR assay. After adding 0, 0.0625, 0.25, 0.5, 0.75, 1, 2 and 4 IU/ml of heparin that was diluted in 20 microl of normal saline to 180 microl of CSF aliquots, CSF total protein concentrations were determined again by the 2 assay systems in the absence or presence of protamine.

At low (<40 mg/dl) and mildly increased (40-or<100 mg/dl) CSF total protein, the measured protein concentrations significantly decreased up to 91% when 4 IU/ml of heparin was added to the samples before being analyzed by the Toshiba TBA-120FR assay. At moderately increased (100-or<200 mg/dl) and high (>or=200 mg/dl) CSF total protein, 62% and 27% decreases were found, respectively. Only 1-8% decline was found when 4 IU/ml of heparin was added to the samples before being analyzed by the Vitros 950 PROT assay. Addition of protamine partially reversed the interference of heparin.

The interference of heparin in the CSF total protein assay is dependent on the reaction principle, especially when the CSF total protein level is normal to mildly elevated.